Preparation

Prepare grill for cooking. If using a charcoal grill, open vents on bottom of grill, then light charcoal. Charcoal fire is medium-hot when you can hold your hand 5 inches above rack for 3 to 4 seconds. If using a gas grill, preheat burners on high, covered, 10 minutes.

Brush both sides of citrus slices with 1/2 tablespoon oil, then brush fish all over with 1 tablespoon oil and season with sea salt and pepper.

Grill citrus slices, covered only if using a gas grill, on lightly oiled grill rack, turning over once, until grill marks appear, 2 to 3 minutes total. Transfer citrus slices to a plate, then, if using a gas grill, reduce heat to moderate. Grill fish, skin sides down, covered only if using a gas grill, until skin is crisp, 3 to 4 minutes. Turn each piece of fish onto 1 side and grill 1 minute. Turn over onto opposite side and grill until fish is just cooked through, 2 to 3 minutes more. Transfer fish to a platter and keep warm, covered loosely with foil.

Heat basil and mint in remaining 1/4 cup oil in a heavy skillet over moderate heat, stirring, until herbs are just wilted, about 1 minute.

Serve fish with herbed oil and top with citrus slices.

Cooks' note:
If you aren't able to grill outdoors, fish and citrus can be cooked in a ridged grill pan. Cook citrus over high heat, then reduce heat to moderately high and cook fish, skin sides down first, turning once, 7 to 8 minutes total.